Methods and system for efficient self-coexistence of wireles regional area networks

ABSTRACT

A method for scheduling self coexistence windows (SCWs), wherein SCWs are part of frames transmitted in wireless regional area networks sharing a common channel, comprises monitoring the common channel for a duration of at least a maximum SCW cycle length; checking if at least one coexistence beacon protocol packet including at least one of SCWs and quiet periods scheduled by neighbor WRANs is detected on the common channel; and establishing a SCW schedule by setting SCW schedule fields in a modified superframe control header, wherein the newly established SCW schedule does not conflict with any already scheduled SCWs and quiet periods.

The invention generally relates to wireless regional area networks. Awireless regional area network (WRAN), as defined by IEEE 802.22 workgroup, is aimed at using cognitive radio techniques. This would allowsharing of geographically unused spectrums allocated to the televisionbroadcast service, on a noninterfering basis, to bring broadband accessto hard-to-reach areas. WRANs are designed to operate in TV broadcastbands, while assuring that no harmful interference is caused to theincumbent operation, i.e., TV broadcasting and low power licenseddevices (e.g., wireless microphones).

FIG. 1 illustrates an exemplary IEEE 802.22 based system 100 thatincludes two WRANs 110 and 120. The base stations (BS 1 and BS 2) maycommunicate with each other over a wide area network (WAN) 130. Acustomer-premises equipment (CPE) in a WRAN can communicate with itsbase station and with a CPE in a neighboring WRAN. For example, CPE Band CPE A in WRAN 110 exchange data with BS 1, and CPE C in WRAN 120communicates with CPE A through channel CBP.

The system 100 can operate in a coexistence mode in which multiple basestations share the same channel. As illustrated in FIG. 2, in such amode of operation, the channel is shared on a per frame basis. That is,a subset of frames 210 in a superframe 200 is allocated to each WRAN ona noninterference basis. In addition, each base station transmits itssuperframe preamble, frame preamble and superframe control header (SCH)during the first active frame allocated to the station. For example,this information would be transmitted by the BS 1 and BS 2 of WRANs 110and 120 during frames 210-0 and 210-1, respectively. The duration ofeach frame 210 is fixed, and each superframe 200 includes a number of‘n’ frames 210 (frames 210-0 through 210-n-1).

The SCH contains information required for orchestrating the transmissionby the base station either in a normal mode or a coexistence mode. Thespecific format of a SCH header is defined in the IEEE 802.22 draft v3.0pages 27 etc., published April 2010.

Each frame 210 may include, at its end, an intra-frame quite period (QP)or self-coexistence window (SCW). The QP or SCW are not necessarilyscheduled to be included in each frame. When an intra-frame QP isscheduled, all stations (i.e., base stations and CPEs) in the WRANs keepsilent during the QP, such that reliable sensing of potential incumbentsignals can be performed. This is needed to protect incumbent signals incognitive radio networks. Generally, the scheduling of the intra-frameQP is achieved by setting the Inter-frame Flag field in the SCH ‘0’ andsetting the field's Intra-frame Quiet Period Cycle Length, Intra-frameQuiet Period Cycle Offset, Intra-frame Quiet period Cycle Frame Bitmap,Intra-frame Quiet Period Duration, and Synchronization Counter forIntra-frame Quiet Period Duration to their appropriate values. The QPscheduling is further described in the above-referenced IEEE 802.22standard.

When a SCW is scheduled, a WRAN can use the SCW to transmit acoexistence beacon protocol (CBP) packet. The CBP packet would includecritical information, such as SCH data and negotiation of frameallocations. The format of a CBP packet 300 is shown in FIG. 3.

The packet 300 includes a CBP preamble 310 and a CBP MAC payload (PDU)320. The CBP MAC PDU 320 contains SCH data 321, a CBP (beacon MAC)header 322, and a predefined number of CBP information elements (IEs)323. By including the SCH data 321 in the CBP MAC PDU 320, thetransmitting CPE or base station conveys necessary information to allowneighbor network discovery and coordination of quiet periods. That is,the SCH advertises the schedule of QPs to CPEs in other neighboringWRANs which may not be able to receive the SCH data directly from otherbase stations. For example, CPE C in WRAN 120 receives the CBP packetincluding a SCH from the CPE A in WRAN 110. It should be noted that CBPpackets can be encapsulated in the IP packets for communication over WAN130.

As the scheduling of intra-frame QPs is defined in the IEEE 802.22,there is no reliable mechanism for scheduling of SCWs disclosed in therelated art. In addition, the current solution for scheduling QPs doesnot allow adjusting QP schedules, for example, to reduce QP duration orQP frequency without causing instability.

Certain embodiments of the invention include a method for schedulingself coexistence windows (SCWs), wherein SCWs are part of framestransmitted in wireless regional area networks (WRANs) sharing a commonchannel, comprises monitoring the common channel for a duration of atleast a maximum SCW cycle length; checking if at least one coexistencebeacon protocol (CBP) packet including at least one of SCWs and quietperiods (QPs) scheduled by neighbor WRANs is detected on the commonchannel; and establishing a SCW schedule by setting SCW schedule fieldsin a modified superframe control header (SCH), wherein the newlyestablished SCW schedule does not conflict with any already scheduledSCWs and QPs. Certain embodiments of the invention further include amethod for scheduling two-hop based Intra-frame quiet periods (QPs),wherein QPs are part of frames transmitted in wireless regional areanetworks (WRANs) sharing a common channel. The method comprisesmonitoring the common channel for a duration of at least a maximum SCWcycle length; checking if at least one coexistence beacon protocol (CBP)packet including at least one intra-frame QP scheduled by neighbor WRANsis detected on the common channel; and establishing an intra-frame QPschedule by setting intra-frame QP schedule fields in a modifiedsuperframe control header (SCH) (700), wherein the establishedintra-frame QP schedule is substantially aligned with any alreadyscheduled QPs. Certain embodiments of the invention also include awireless device that comprises a signal sensing module for identifyingCBP packets transmitted on a common channel; a scheduler for analyzingthe CBP packets to determine if self-coexistence windows (SCWs) or quietperiods (QPs) can be scheduled and for scheduling at least one ofcontention-based SCWs, reservation-based SCWs, and intra-frame QPs; asignal transceiver; and a spectrum manager for managing the commonchannel and controlling the transceiver to transmit CBP packets inscheduled SCWs or to halt any transmission during QPs.

The subject matter that is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe invention will be apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings.

FIG. 1 is a diagram of an exemplary IEEE 802.22 communication system;

FIG. 2 is an illustration of a superframe structure in a coexistencemode;

FIG. 3 is an illustration of a CPB packet format;

FIG. 4 is a flowchart illustrating a method for establishing areservation-based SCW schedule in accordance with an embodiment of theinvention;

FIG. 5 is a flowchart illustrating a method for establishing acontention-based SCW schedule in accordance with an embodiment of theinvention;

FIG. 6 is a flowchart illustrating a method for establishing anintra-frame QP schedule in accordance with an embodiment of theinvention;

FIG. 7 is an illustration of a modified SCH format; and

FIG. 8 is a block diagram of a wireless device in accordance with anembodiment of the invention.

It is important to note that the embodiments disclosed by the inventionare only examples of the many advantageous uses of the innovativeteachings herein. In general, statements made in the specification ofthe present application do not necessarily limit any of the variousclaimed inventions. Moreover, some statements may apply to someinventive features but not to others. In general, unless otherwiseindicated, singular elements may be in plural and vice versa with noloss of generality. In the drawings, like numerals refer to like partsthrough several views. Various embodiments of the invention include amethod for scheduling a contention-based SCW and a reservation-basedSCW. As mentioned above, a SCW is part of a frame and may be included insome of the frames of a superframe. In a contention-based scheduling,the SCW is shared by neighbor WRANs. In reservation-based scheduling,the WRAN reserving a SCW has an exclusive access to the reserved SCW.

To perform SCW scheduling, the SCH is modified to include the followingfields: SCW Cycle Length, SCW Cycle Offset, and SCW Cycle Frame Bitmap.An exemplary diagram of the modified SCH format is shown in FIG. 7. TheSCW Cycle Length field represents, in number of superframes, the cycleinterval length between each successive superframe carrying SCWs. Ifthis field is set to 0, then no SCW cycle is scheduled. In accordancewith one embodiment, the SCW Cycle Length field is set to one of fivefollowing predefined values: 1, 2, 4, 8, and 16. For example, if thisfield is set to 1, a SCW Cycle repeats every superframe, if the field isset to 2, a SCW Cycle repeats every 2 superframes, and so on. In anexemplary embodiment, the size of the SCW Cycle Length field is 5 bits.

The SCW Cycle Offset field specifies, as a number of superframes, theoffset from the superframe carrying the SCH to the superframe where theSCW cycle should start or repeat. For example, if this field is set to0, the SCW cycle starts from the current superframe, i.e., thesuperframe contains the SCH. The value of the SCW Cycle Offset fieldshould be less than a value of the SCW Cycle length field, unless in aninitial countdown state. In the initial countdown state, this field canbe equal to or be larger than the value of the SCW Cycle Length field.It should be noted that a bigger initial countdown number allowsneighbor WRANs to discover and avoid any potential SCW reservationcollision. In an exemplary embodiment, the size of the SCW Cycle Offsetfield is 8 bits.

The SCW Cycle Frame Bitmap field specifies which frames in a scheduledsuperframe include a scheduled SCW and the SCW mode (i.e.,reservation-based or contention-based). In accordance with an embodimentof the invention, each 2-bit in the Bitmap field is used to indicatefour possible scheduling states of a frame: 1) no SCW scheduled; 2) areservation-based SCW; 3) a reservation-based SCW scheduled by adirect-neighbor WRAN; and 4) a contention-based SCW.

In an exemplary embodiment of the invention, each 2-bit in the SCW CycleFrame Bitmap is encoded as illustrated in Table 2. The current WRAN isthe network that performs the scheduling method and a direct-neighborWRAN is a neighbor of the current WRAN.

TABLE 2 2-Bit Value Scheduling type 00 no SCW scheduled 01contention-based SCW by the current WRAN 10 reservation-based SCW by adirect-neighbor WRAN 11 reservation-based SCW by the current WRAN

In one embodiment of the invention, a fairness policy is applied tolimit the number of reservation-based SCWs per WRAN and per SCW Cycle.In addition, to ensure minimum conditions for operation, at least acertain number (e.g., 1) of contention-based SCWs should be scheduled inone SCW cycle. Base stations may start scheduling their contention-basedSCWs from the last frame of the superframe, going backward for multiplecontention-based SCWs. This ensures more uniform and easier to convergescheduling. It should be noted that if SCW scheduling conflicts with aQP in a given frame, the QP overrides the SCW.

According to certain aspects of the invention, the SCW schedulingparameters in the SCH are transmitted by a base station. This ensuresreliable transmission of such information to all CPEs. The CPEs can useCBP packets to transmit the SCW schedule information to its neighboringWRANs. It should be noted that CBP packets containing SCH may begenerated directly by a base station and then transmitted to the CPEs.In such case, the CPEs need only to relay the CBP packets, instead ofgenerating CBP packets by themselves. A base station or CPE in anotherWRAN may receive CBPs from the BS or CPEs.

FIG. 4 shows a non-limiting flowchart 400 illustrating a method forscheduling reservation-base SCWs in accordance with an embodiment of theinvention. As mentioned above, a WRAN reserving a reservation-based SCWhas an exclusive access to the SCW. This allows contention-freetransmissions of CBP packets among neighbor WRANs sharing the samechannel.

At S410, during the initialization stage of a WRAN attempting toschedule SCWs, the channel is monitored for the duration of at least amaximum SCW Cycle Length (e.g., at least 16 superframes). This isperformed for the purpose of discovering neighbor WRANs and identifyingtheir scheduled SCWs and QPs. The schedules are specified in CBP packetssent by one or more neighboring WRANs.

At S420, a check is made to determine if one or more SCWs and/or QPsscheduled by neighboring WRANs are detected. The scheduled SCWs aredesignated in a SCW Cycle Frame Bitmap field, where, for example, the2-bit of a corresponding reserved frame is set to 11 or 10. If S420results in an affirmative answer, at the S430, the frames with reservedSCWs and QPs are marked and cannot be used as reservation-based SCWs bythe WRAN attempting to schedule reservation-based SCWs. Thus, the methodensures that no overlapping SCWs exist.

If S420 results in a negative answer, execution proceeds to S440 where aSCW schedule is established by setting the SCW schedule fields in theSCH. Specifically, the values of the SCW Cycle Offset field arepreferably set to be larger than a value of the SCW Cycle Length field,and each 2-bit in the SCW Cycle Frame Bitmap field corresponding to aframe to be reserved is set to a value of 11.

At S450, the WRAN conveys its SCW schedule to neighboring WRANs bytransmitting CBP packets (including the SCH) via contention-based SCWsscheduled by neighbor WRANs. It should be noted that the SCW schedulecan be adjusted at any time by updating the values of the SCW schedulefields set at S440. The method may be performed by a base station, wheremonitoring of the channel is done, in part, by the CPEs in the WRAN.

In accordance with an embodiment of the invention, potential reservationconflicts after scheduling of reservation-based SCWs can be detected.According to this embodiment, the WRAN can purposely skip thetransmission of a CBP packet in its reserved SCWs and schedule one CPEin the network to listen to the channel during the reserved SCWs. If areservation conflict is identified, the WRAN will restart the process ofscheduling SCWs.

FIG. 5 shows a non-limiting flowchart 500 illustrating a method forscheduling contention-based SCWs in accordance with another embodimentof the invention. As mentioned above, a contention-based SCW can beshared by neighbor WRANs. The method is performed by a WRAN which willbe the owner of the scheduled SCWs.

At S510, during the initialization stage of the owner WRAN, the channelis monitored for the duration of at least a maximum SCW Cycle Length(e.g., at least 16 superframes) in order to discover neighbor WRANs andidentify their scheduled SCWs and QPs. The schedules are specified inCBP packets sent by one or more neighboring WRANs.

At S520, a check is made to determine if reservation-based SCWs and/orcontention-based SCWs and/or QPs scheduled by other WRANs are detected.The reserved SCWs are specified in a SCW Cycle Frame Bitmap field,where, for example, the 2-bit is set to 11 or 10 in the correspondingframe. If S520 results in an affirmative answer, at the S530, the frameswith reserved SCWs and QPs are marked and cannot be used ascontention-based SCWs by the owner WRAN.

If S520 results in a negative answer, execution proceeds to S540, wherea contention-based SCW schedule is established by setting the SCWschedule field in the SCH. Specifically, at S540, the value of the SCWCycle Offset field is preferably set to be larger than the value of theSCW Cycle Length field. In addition, each 2-bit in the SCW Cycle FrameBitmap field corresponding to a frame that should include acontention-based SCW is set to a value of 01. At S550, the WRAN conveysits SCW schedule to neighboring WRANs by transmitting CBP packets(including the SCH). It should be noted that the SCW schedule can beadjusted at any time by updating the values of SCW schedule fields setat S540.

Contention-based SCWs can be shared by neighbor WRANs. That is,neighbors of the owner WRAN (same as the owner WRAN) can use thecontention-based SCWs for the transmission of CBP packets following therandom backoff mechanisms. However, the owner WRAN has the ownership ofits scheduled contention-based SCWs and other WRANs neither can usethose SCWs for other purposes of transmissions nor can the other WRANscancel the SCWs' schedules. The owner WRAN can reduce the frequency ofcontention-based SCWs by cancelling some, but not all, of the scheduledcontention-based SCWs.

In an embodiment of the invention, two neighbor WRANs can be theco-owner of a certain set of contention-based SCWs by scheduling them intheir SCHs. In this embodiment, if one WRAN cancels the scheduledcontention-based SCWs, it does not affect the other WRAN. Therefore, theWRAN having the active schedule, as well as its neighbor WRANs, canstill share contention-based SCWs.

According to certain aspects of the invention, a method to mitigatecollision of contention among neighboring WRANs while accessing acontention-based SCW is provided. To mitigate collision of contentionwith neighboring WRANs, an access to a contention-based SCW should bepreceded by a random backoff in a unit of contention-based SCWs.Specifically, when a base station schedules its associated CPEs totransmit CBP packets via contention-based SCWs, the base station waitsfor a random number (e.g., from 0 to 15 with identical probability) ofnext available contention-based SCWs. For example, if the random numberchosen is 0, the base station schedules a

CBP transmission via an US-MAP information element (IE) by accessing thefirst available contention-based SCW from the transmission of the US-MAPIE. If the random number is 5, the base station schedules a CBPtransmission via a US-MAP IE by accessing the sixth availablecontention-based SCWs from the transmission of the US-MAP IE. A US-MAPIE is an IE transmitted from a base station to CPEs to schedule thetransmissions (e.g., CBP transmissions to other WRANs) or otheractivities (e.g., CBP receptions from other WRANs) of CPEs.

Multiple WRANs operating on the same channel may share SCWs. Sharing ofSCWs may reduce the total overhead in the channel. On the other hand,reservation of SCWs enables contention-free CBP packet transmissions.The decision on whether to share or reserve SCWs depends on the totaloverhead generated by SCWs and the coexistence scenarios. Moreover, theWRANs may change their schedule of SCWs dynamically, and therefore WRANsmay adjust the schedule to adapt to coexistence scenarios.

FIG. 6 shows a non-limiting flowchart 600 illustrating the method forestablishing two-hop based Intra-frame QP schedules in accordance withone embodiment of the invention. As mentioned above, during the QP nodevice in any WRAN is allowed to transmit data. To allow this type ofscheduling the following fields in the SCH have been modified to carryinformation related to the new QP scheduling method: Intra-frame QuietPeriod Cycle Length, Intra-frame Quiet Period Cycle Offset, Intra-frameQuiet period Cycle Frame Bitmap, and Intra-frame Quiet Period Duration.The modified SCH format is illustrated in FIG. 7.

The Intra-frame Quiet Period Cycle Length field specifies the number ofsuperframes for which the intra-frame sensing specification is valid. Ifthis field is set to 0, no intra-frame quiet period is scheduled or thecurrent intra-frame quiet period schedule is canceled. This field shouldbe set to an integer number greater than 1 to be effective. In oneembodiment, the field can be set to one of the following values 1, 2, 4,8, and 16. In an exemplary embodiment, the size of the field is 5 bits.

Intra-frame Quiet Period Cycle Offset field is valid only if intra-frameQuiet Period Cycle Length is greater than 0 and is used for in-bandintra-frame sensing. This field indicates, as a number of superframes,the offset from a SCH transmission to the beginning of the superframewhere the QP cycle starts or repeats. The value of the field should beless than Intra-frame Quiet Period Cycle length unless in an initialcountdown state. In the initial countdown state, this field may includea value equal or larger than a value of the Intra-frame Quiet PeriodCycle Length field. In an exemplary embodiment, the size of theIntra-frame Quiet Period Cycle Offset field is 8 bits.

Intra-frame Quiet period Cycle Frame Bitmap field indicates if a QPshould be part of the frame and if so by which WRAN. In an embodiment ofthe invention, each 2-bit in the Bitmap field corresponds to one framewithin the superframe encoded as listed in Table 3.

TABLE 3 2-Bit Value QP Scheduling type 00 no QP scheduled 01 Reserved 10QP by a direct-neighbor WRAN 11 QP by the current WRAN

The current WRAN is the network that performs the scheduling method, anda direct-neighbor WRAN is a neighbor of the current WRAN. In anexemplary embodiment, the size of this Bitmap field is 32 bits.

Intra-frame Quiet Period Duration field indicates the number of symbols(2̂x: x specified by this field) starting from the end of the frameduring which no transmission should take place. For example, if thisfield is set to 4, the intra-frame Quiet Period duration equals to 16symbols. In an exemplary embodiment, the size of this Duration field is8 bits.

Referring back to FIG. 6, at S610, during the initialization stage ofthe WRAN attempting to establish QP schedule (the current WRAN), thechannel is monitored for the duration of a maximum SCW Cycle Lengthfield (e.g., at least 16 superframes) in order to discover neighboringWRANs and identify their scheduled QPs. The schedules are specified inCBP packets or frames including a SCH and sent by one or moreneighboring WRANs.

At S620, a check is made to determine if one or more intra-frame QPsscheduled by other WRANs are detected. The schedule of QPs is specifiedin the Intra-frame Quiet Period Cycle Frame Bitmap field within themodified SCH format 700. Each 2-bit in the Bitmap corresponds to oneframe in the superframe specified by Intra-frame QP Cycle field. If the2-bit is set to 11, an intra-frame QP is scheduled by the first hopneighbor WRAN. If the 2-bit is set to 10, an intra-frame QP is scheduledby a second hop neighbor WRAN. If S620 results in an affirmative answer,at the S630, QPs reserved with frames are marked. It should be notedthat if SCWs scheduled by other WRANs are detected, those SCWs should beprotected by not scheduling QPs overlapping with those SCWs.

If S620 results in a negative answer, execution proceeds to S640, wherean intra-frame QP schedule is established by setting the intra-frame QPschedule fields in the SCH. Specifically, at S640, a value of theIntra-frame QP Cycle Offset field is preferably set to be larger than avalue of the Intra-frame QP Cycle length field. In addition, each 2-bitin the Intra-frame QP Cycle Frame Bitmap field corresponding to a frameto be reserved is set to a value of 11. When establishing QP schedule,an attempt is made to align and thus synchronize the new schedule withQPs marked at S630.

At S650, the WRAN conveys its intra-frame QP schedule to neighboringWRANs by transmitting CBP packets (including the SCH) via contentionbased SCWs scheduled by neighboring WRANs. It should be noted that theintra-frame QP schedule can be adjusted at any time by updating thevalues of intra-frame QP schedule fields set at S640.

According to certain aspects of the invention, the method forestablishing a QP schedule described herein allows reusing QPs amongtwo-hop neighbor WRANs while keeping independence and flexibility toadjust the QP schedule (e.g., reducing QP duration or QP frequency)without causing instability. QPs can be shared and are protected byneighbor WRANs. That is, neighbor WRANs of a WRAN that scheduled the QPs(the current WRAN) can use and should protect these QPs for spectrumsensing. The current WRAN has the ownership over the scheduled QPs.Thus, other WRANs neither can use the QPs for other purposes oftransmissions nor can they cancel the schedules of QPs. The current WRANcan reduce the frequency of QPs by canceling some QPs.

In an embodiment of the invention, two neighboring WRANs can be theco-owners of a certain set of intra-frame QPs by scheduling them intheir SCHs respectively. In this embodiment, if one WRAN cancels thescheduled QPs, it does not affect the other WRAN. Therefore, the WRANhaving the active schedule, as well as its neighbor WRANs, can stillshare scheduled QPs.

FIG. 7 shows an exemplary and non-limiting diagram of a modified SCHformat structure 700 constructed in accordance with an embodiment of theinvention. The SCH fields 701 through 712, 722 and 723 are defined inthe above-referenced IEEE 802.22 standard. The Intra-frame Quiet PeriodCycle Length field 713, Intra-frame Quiet Period Cycle Offset field 714,Intra-frame Quiet period Cycle Frame Bitmap field 715, and Intra-frameQuiet Period Duration field 716 are used for the intra-frame QPscheduling as shown in FIG. 6 and carry the information described indetail above. The reserved field 717 includes bits set to ‘0’. Thevalues in fields 710 through 716 are set according to the Inter-frameFlag field 709. If the field's 709 value is ‘1’, a first inter-frame QPscheduling and then intra-frame QP scheduling are performed, and thevalues in field 710 and 711 are set to their respective values.Otherwise, the fields 713 and 716 are set for intra-frame QP scheduling.The SCW Cycle Length field 718, SCW Cycle Offset field 719, and SCWCycle Frame Bitmap field 720 are set for either reservation-based SCW orcontention-based SCW as described in detail above. The reserved field721 includes bits set to ‘0’.

FIG. 8 shows an exemplary and non-limiting block diagram of a wirelessdevice 800 constructed in accordance with an embodiment of theinvention. The wireless device 800 includes a spectrum manager 810, ascheduler 820 coupled to a signal sensing module 830, and a signaltransceiver 840. The signal sensing module 830 identifies CBP packetstransmitted by other WRANs and provides captured CBP packets to thescheduler 820. The scheduler 820 analyzes the CBP packets to determineif SCWs or QPs can be scheduled. The scheduler 820 is adapted to performthe method for establishing and adjusting contention-based SCW,reservation-based SCW, and intra-frame QPs scheduling as described indetail above. The spectrum manager 810 controls the transceiver 840 tomanage channels and to transmit CBP packets in scheduled SCWs or to haltany transmission during QPs. The device 800 may be implemented either ina base station or a CPE.

The embodiments disclosed herein can be implemented in any IEEE 802.22based system or in any other cognitive radio system.

The principles of the invention can be implemented as hardware,firmware, software or any combination thereof. Moreover, the software ispreferably implemented as an application program tangibly embodied on aprogram storage unit, a non-transitory computer readable medium, or anon-transitory machine-readable storage medium that can be in a form ofa digital circuit, an analogy circuit, a magnetic medium, or combinationthereof. The application program may be uploaded to, and executed by, amachine comprising any suitable architecture. Preferably, the machine isimplemented on a computer platform having hardware such as one or morecentral processing units (“CPUs”), a memory, and input/outputinterfaces. The computer platform may also include an operating systemand microinstruction code. The various processes and functions describedherein may be either part of the microinstruction code or part of theapplication program, or any combination thereof, which may be executedby a CPU, whether or not such computer or processor is explicitly shown.In addition, various other peripheral units may be connected to thecomputer platform such as an additional data storage unit and a printingunit.

The foregoing detailed description has set forth a few of the many formsthat the invention can take. It is intended that the foregoing detaileddescription be understood as an illustration of selected forms that theinvention can take and not as a limitation to the definition of theinvention. It is only the claims, including all equivalents that areintended to define the scope of this invention.

1. A method for scheduling self coexistence windows (SCWs), wherein SCWsare part of frames transmitted in wireless regional area networks(WRANs) sharing a common channel, the method comprising: monitoring thecommon channel for a duration of at least a maximum SCW cycle length;checking if at least one coexistence beacon protocol (CBP) packetincluding at least one of SCWs and quiet periods (QPs) scheduled byneighbor WRANs is detected on the common channel; and establishing anSCW schedule by setting SCW schedule fields in a modified superframecontrol header (SCH), the SCW schedule fields comprising an SCW cyclelength field that indicates a number of superframes to be transmittedbetween each superframe carrying an SCW.
 2. The method of claim 1,further comprising conveying a reservation-based SCW schedule toneighbor WRANs.
 3. The method of claim 2, further comprising adjustingthe reservation-based SCW schedule by updating values of the mode field.4. The method of claim 1, wherein the SCW schedule fields furthercomprise an SCW Cycle Offset field, and an SCW Cycle Frame Bitmap field.5. The method of claim 4, wherein the self coexistence windows (SCWs)are reservation-based SCWs.
 6. The method of claim 5, wherein settingthe SCW schedule fields further comprises setting a value of the SCWCycle Offset field to a number of superframes greater than a number ofsuperframes assigned in the SCW Cycle Length field; and setting every 2bits in the SCW Cycle Frame Bitmap field corresponding to a frame to bereserved to a value indicating a reservation-based SCW.
 7. The method ofclaim 6, wherein an owner WRAN has exclusive access to reservation-basedSCWs indicated in the SCW schedule.
 8. The method of claim 4, whereinthe self coexistence windows (SCWs) are contention-based SCWs.
 9. Themethod of claim 8, wherein setting the SCW fields further comprises:setting a value of the SCW Cycle Offset field to a number of superframesgreater than a number of superframes assigned in the SCW Cycle Lengthfield; and setting every 2 bits in the SCW Cycle Frame Bitmap fieldcorresponding to a frame to be scheduled to a value indicating acontention-based SCW.
 10. The method of claim 9, wherein an owner WRANshares contention-based SCWs with its neighbor WRANs.
 11. The method ofclaim 10, wherein each neighbor WRAN can transmit CBP packets incontention-based SCWs after waiting a random backoff time.
 12. Awireless device, comprising: a signal sensing module configured toidentify co-existing beacon protocol (CBP) packets transmitted on acommon channel; a scheduler configured to analyze the CBP packets todetermine if self-coexistence windows (SCWs) or quiet periods (QPs) canbe scheduled and to schedule at least one of contention-based SCWs,reservation-based SCWs, and intra-frame QPs, the scheduler being furtherconfigured to schedule the contention-based SCWs or reservation basedSCWs by adjusting SCW schedule fields in a superframe control header,the SCW schedule fields further comprising an SCW cycle length fieldthat indicates a number of superframes to be transmitted between eachsuperframe carrying a n SCW; a signal transceiver; and a spectrummanager for managing the common channel and controlling the transceiverto transmit CBP packets in scheduled SCWs or to halt any transmissionduring QPs.
 13. The wireless device of claim 12, wherein to adjust theSCW schedule fields the scheduler is configured to: set a value of anSCW Cycle Offset field to a number of superframes greater than a numberof superframes assigned in an SCW Cycle Length field; and set every 2bits in an SCW Cycle Frame Bitmap field corresponding to a frame to bereserved to a value indicating a reservation-based SCW.